Porous aluminide structures have potential applications in a variety of fields. For example, they serve as filter devices at temperatures above 400.degree. C. Furthermore, porous aluminide structures form excellent catalyst supports for cleaning gases in catalytic converters. Furthermore, these structures provide excellent fuel cell anodes. The high temperature strength, oxidation resistance and phase stability of the intermetallic nickel aluminide allow these porous structures to serve in these environments.
Van Beijnen et al., in U.S. Pat. No. 5,238,755, disclose a process for forming a fuel cell from a combination of carbonyl nickel powder (1 to 10 .mu.m) and intermetallic powder (1 to 10 .mu.m). This fuel cell structure has very little, if any, porosity. A. L. Baldi, in U.S. Pat. No. 5,077,257, discloses a method of forming porous metal aluminide catalysts from aluminum powder mixed with a powdered pyrophorically activated material (nickel). The process first causes the nickel and aluminum to react. Then it leaches out the aluminum with a solution containing 20% sodium hydroxide to render the remainder a pyrophoric structure. Finally, burning this pyrophoric structure leaves a porous nickel aluminide catalyst.
Pierotti et al., in U.S. Pat. No. 4,990,181, disclose a method of forming porous aluminide structures. This process mixes nickel powder, aluminum powder and cellulose and extrudes them as a green structure. After drying this green structure at 100.degree. C., sintering the dried structure, at 1300.degree. C., in argon atmosphere "burns out" the cellulose and reacts the nickel and aluminum to produce a porous aluminide structure. This process claims the ability to produce aluminide substrates having a porosity between 25 and 75 volume percent from metal powders.
T. Toshiyasu et al., in U.S. Pat. Nos. 5,582,867 and 5,672,387, disclose a method of manufacturing nickel-chromium aluminum foams. This process starts with surrounding nickel foam with powders of aluminum, chromium and NH.sub.4 Cl in a chamber containing Ar and H.sub.2. Raising and lowering the temperature within the chamber controls the chamber ratio of aluminum to chromium deposited on the nickel product. This pack diffusion process often requires several hours to deposit sufficient chromium and aluminum to form oxidation resistant foams.
It is an object of this invention to provide a method of making high porosity open nickel-aluminum and nickel aluminide structures.
It is a further object of this invention to provide a method of making reinforced porous nickel-aluminum and nickel aluminide structures.
It is a further object of this invention to produce a powder-free method of forming porous nickel-aluminum and nickel aluminide structures.
It is a further object of this invention to provide a method of making porous nickel-aluminum and nickel aluminide structures having controlled porosities.